1. Field of the Invention
This invention relates in general to methods of refining and deodorizing edible oils and fats and, more particularly, to methods of refining to prevent auto-oxidation of edible oils and fats.
2. Description of the Prior Art
In the past, refining of edible oils has generally been a batch or semi-continuous processes. Thus, bleaching, degumming, deaerating, vacuum distillation, caustic refining and other steps have been performed in either separate steps or in steps which hold large volumes of oil for relatively long periods. During such processes it is necessary to protect the oil from auto-oxidation. Auto-oxidation is the formation of peroxide bonds and hydroperoxide bonds in the fatty acid chain as a result of oxygen dissolved in the oil, oxygen in the air contacting the oil, and hydrolysis of water in oil. If auto-oxidation occurs, the oil becomes unstable and rancid.
The present methods of protecting the oil from auto-oxidation include deaeration and the addition of anti-oxidants. Deaeration, when it has been used, has been achieved by subjecting the oil to a vacuum in a holding vessel. It is necessary to hold the oil in a vessel for several minutes in order to achieve the deaeration. Deaeration processes are shown in U.S. Pat. No. 2,691,665 to Bailey and in U.S. Pat. No. 4,089,880 to Sullivan. The Bailey patent shows an oil deaeration in the deodorization stage and the Sullivan patent shows an oil deaeration in the bleaching stage.
In conjunction with deaeration, common method of protecting the oil against auto oxidation is to add anti-oxidants to the oil. Such anti-oxidants include BHA, BHT, THBP and TBHQ. A particular problem with adding anti-oxidants is that such anti-oxidants are relatively expensive and are of unknown toxicity.
Protecting the oil against auto-oxidation becomes especially important as the natural anti-oxidants in the oil such as phosphatides and tocopherol are removed from the oil. Generally, phosphatides are removed from the oil by a degumming step and tocopherol is removed from the oil during caustic refining or vacuum steam refining. Deaeration of the oil as used in the past generally occurs during steam refining or deodorization. Of course, the longer the oil remains unprotected after natural anti-oxidants are removed, the more auto-oxidation will occur. The addition of anti-oxidants as used in the past generally occurs after the oil is completely refined and prior to shipping in order to protect the oil from becoming rancid.
The methods of protecting the oil against auto-oxidation of the past have not been entirely satisfactory. Particularly, they have been less efficient, more expensive and less effective than is desirable.
The present invention provides an improved method of refining with prevents auto-oxidation of oil associated with refining and deodorization and thereafter. This method is especially useful with the method of continuous refining and deodorization disclosed in my co-pending patent application Ser. No. 540,037 filed Oct. 7, 1983. In order to provide a more complete understanding of the present invention and the art of edible oil refining in general, reference may be had to this co-pending application, the disclosure of which is incorporated herein by reference.